ijmb model questions vol1 2017 biology | Practical

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Question 1 View Details
A prepared slide of a thin transverse section of onion epidermis has been stained with iodine solution. Using a compound microscope with a 10× ocular lens, the student selects the 40× objective lens. The microscope is equipped with a calibrated ocular micrometer in which the scale bar on the captured image measures 1.0 cm and represents 20 µm at the total magnification used. The student measures the length of a central vacuole on the image as 0.45 cm. Perform the following tasks:
Question Parts
(a)
Calculate the actual length of the vacuole in micrometres (µm).
(b)
Identify any three organelles that can be clearly observed in the slide and state one function for each.
(c)
List two possible sources of error that could affect the measurement obtained in part (a).
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Question 2 View Details
A student investigates the effect of colchicine on mitosis in the root tip cells of Allium cepa (onion). Three sets of root tips are prepared: 1. Control (no colchicine) 2. 0.1 % colchicine solution for 4 h 3. 0.5 % colchicine solution for 4 h For each set, 200 cells are examined under a microscope and the numbers of cells observed in the four stages of mitosis are recorded as shown in the table. | Treatment | Prophase | Metaphase | Anaphase | Telophase | |-----------|----------|-----------|----------|-----------| | Control | 30 | 20 | 15 | 10 | | 0.1 % | 20 | 35 | 10 | 5 | | 0.5 % | 10 | 45 | 5 | 5 | Tasks: a) Calculate the mitotic index for each treatment. (Mitotic index = (total number of cells in all mitotic stages / total cells examined) × 100%). b) Identify which treatment shows the highest mitotic index. c) Explain the observed effect of colchicine on the distribution of cells among the mitotic stages. d) Suggest one precaution that should be observed when preparing the colchicine solutions to avoid experimental artefacts.
Question Parts
(a)
Calculate the mitotic index for each treatment.
(b)
State which treatment has the highest mitotic index.
(c)
Explain the effect of colchicine on the distribution of cells among the mitotic stages observed.
(d)
Suggest one precaution that should be observed when preparing the colchicine solutions.
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Question 3 View Details
A student is investigating the carbohydrate content of a powdered food sample using Benedict's test. The procedure is as follows: 1. Prepare a standard glucose solution by dissolving 0.50 g of pure glucose in 100.0 mL of distilled water. 2. Take 5.0 mL of the standard solution, add 5.0 mL of Benedict's reagent, heat in a boiling water bath for 5 minutes and allow the precipitate to cool. After drying, the precipitate weighs 0.025 g. 3. Weigh 2.00 g of the powdered food sample, grind it finely and extract with 50.0 mL of distilled water. Filter the mixture and take 5.0 mL of the filtrate, treat it exactly as in step 2. The dried precipitate from this unknown sample weighs 0.018 g. Using the data above, answer the following questions:
Question Parts
(a)
Calculate the concentration of the standard glucose solution in grams per millilitre (g mL⁻¹).
(b)
Determine the percentage (w/w) of carbohydrate present in the powdered food sample.
(c)
Identify two possible sources of systematic error in this experiment and explain how each would affect the calculated carbohydrate percentage.
(d)
Suggest one procedural improvement that could increase the reliability of the result.
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Question 4 View Details
A group of students set up a closed respirometer to study the effect of temperature on the rate of respiration in germinating beans. The apparatus consists of a sealed container holding 10.0 mL of 3‑day‑old mung beans immersed in 100.0 mL of distilled water. As the beans respire, oxygen is consumed and water is displaced. The volume of displaced water is recorded after 30 minutes at each temperature. Data recorded: - At 25 °C, displaced water = 12.0 mL. - At 35 °C, displaced water = 18.0 mL. Assume that the volume of displaced water equals the volume of O₂ consumed. Answer the following questions:
Question Parts
(a)
Calculate the rate of oxygen consumption (in mL h⁻¹) at 25 °C and at 35 °C.
(b)
Determine the temperature coefficient (Q₁₀) for the respiration process between 25 °C and 35 °C using the formula Q₁₀ = (R₂/R₁)^{10/(T₂‑T₁)}.
(c)
Interpret the Q₁₀ value obtained in part (b) in terms of the temperature sensitivity of the bean respiration.
(d)
Identify two procedural errors that could lead to an under‑estimation of the true respiration rate and explain their effect.
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